A laser is a device that emits light (electromagnetic radiation) through a process of optical amplification based on the stimulated emission of photons. A fiber laser is a laser in which the active gain medium is an optical fiber doped with rare-earth elements. They are related to doped fiber amplifiers, which provide light amplification without lasing. Fiber nonlinearities, such as Stimulated Brillouin Scattering (SBS), stimulated Raman scattering or four-wave mixing can also provide gain and thus serve as gain media for a fiber laser.
Recent advances in fiber lasers have made them a leading candidate for various applications. To achieve required power levels needed for certain laser applications it may be necessary to combine a large number of lasers for efficient propagation over distances of many kilometers. Fiber lasers can be combined spectrally, coherently, or incoherently.
For intense laser beams travelling in a medium such as an optical fiber, the variations in the electric field of the beam may produce acoustic vibrations in the medium via electrostriction. The beam may undergo Brillouin scattering from these vibrations, usually on opposite direction to the incoming beam, a phenomenon known as Stimulated Brillouin Scattering (SBS). Stimulated Brillouin scattering is one effect by which optical phase conjugation can take place.
For the past few decades, stimulated Brillouin scattering (SBS) in optical fibers has been vigorously investigated in optical fibers. SBS has been used successfully in the past to combine and clean up an aberrated beam Research conducted in the last few years have been successful in combining two beams from mutually incoherent sources. Recently it has been demonstrated that the output from two fiber amplifiers can be successfully phased and combined using SBS. The task remains to efficiently combine more than two beams.
In the prior art various means have been suggested to combine multiple laser beams into a single frequency. One such method is to use unseeded Stimulated Brillouin Scattering (SBS) combination in a multi rode GRIN fiber. Such method utilizes a single core GRIN fiber and unseeded beam for combining incoherent beams from district and non-phase controlled diode lasers. Disadvantage of such method is low conversion efficiency due to poor SMS signal/pump signal overlap and high SBS threshold in the large nonlinear fiber.
A need, therefore, exists for an improved way to incoherently combine multiple pump lasers in a single optical fiber. There is also a need for a high efficient, scalable, high brightness laser source. In addition, improving the signal/pump overlap area greatly improves conversion efficiency.